FIG. 1 shows a plan structure of a conventional active matrix organic light emitting device (AMOLED), focusing on a pixel consisting of red (R), green (G) and blue (B) unit pixels.
Referring to FIG. 1, the conventional AMOLED includes a plurality of gate lines 110 insulated from each other and arranged in a direction, a plurality of data lines 120 insulated from each other and arranged in a direction crossing with the gate lines 110, and a power line 130 crossing with the gate lines 110, arranged in parallel with the data lines 120 and insulated from each other. The AMOLED also includes, a plurality of pixel portions 140 formed by the gate lines 110, the data lines 120 and the power line 130, and a plurality of pixel electrodes 150 having an opening 155 arranged in each of the pixel portions 140.
Though not shown in the drawings, R, G and B unit pixels are arranged in each of the pixel portions 140, and each pixel unit includes a thin film transistor, a capacitor and an electroluminescence (EL) device coupled to the pixel electrode 150. A via hole 160 connects the pixel electrode 150 with one of the source electrode and the drain electrode of the thin film transistor.
The conventional organic light emitting device having a plan structure described above may have a problem with decreased contrast when the EL device emits light, since exterior light is reflected by metal materials, such as a gate electrode, the source and drain electrodes of the thin film transistor, a capacitor electrode, and other wiring. A mobile display which is extensively exposed to exterior light may have a problem of decreased contrast due to the high reflectivity of the exterior light.
In order to prevent the decreased contrast by reflection of the exterior light, a polarizer may be attached to the front surface of the display. However, using the polarizer may result in increased production cost, as well as decreased transmittance that degrades the contrast, because the polarizer itself shields light emitted from the organic emission layer.
Alternatively, a black matrix composed of Cr/CrOx, or an organic layer, is separately formed on an area in which the TFT and the capacitor are formed. A separate mask process may be required, however, to form the black matrix, making the manufacturing process relatively complicated.
When the contrast is improved by decreasing the reflectivity based on the exterior light, it may be important to more strenuously implement black than white. Korean patent application No. 2001-0085187 has disclosed a technique with which the black matrix is formed by using a concentration gradient layer (MIHL, metal insulator hybrid layer) in the active matrix organic light emitting device of a bottom-emitting type. However, this technique requires a separate process to form the black matrix.